Thanks for the information, I was not aware of that.
Unfortunately, this FM does not exists in the system. Maybe is just a matter of implementing a OSS note.
Anyway, I already made use of another FM (SSFW_KRN_SIGN, the newest version of SSF_KRN_SIGN I guess) which rescued me in another cryptographic problem.
This problem was solved with SSF_KRN_ENVELOPE (I will post the problem in another reply).
Regards.